The first time I turned some case necks [ 30BR ] I was really worried about possibly having removed too much metal at the neck to shoulder joint. I decided to section a case for piece of mind. I have a couple of 'Razor Saws' left over from the modeling days and they worked perfectly. You still need to deburr the edges so you get an accurate idea of the thickness of the remaining metal.
Below are some pics showing some sectioned cases and the saw I use.
Below are some pics showing some sectioned cases and the saw I use.